We had an old version under "contested settings" and it looks like some
of them were modified. I hope that our new, separate file will
discourage manual tweaks.
We can include the relaxed rules from a gem as well. Let's see if we
need that complexity one day.
It's now just called `mode`. This avoids the warning:
../app/models/spree/gateway.rb:31:in `provider': Base#gateway_mode is deprecated in favor of Base#mode and will be removed in a future version